8. solution: suppose there are x pear trees, which is derived from the meaning of the question

X+ 12×4= 168

The solution is X= 120.

9. Solution: Let the weight of yellow cattle be X kg and the weight of blue whale be Y kg.

5 tons =5000KG, 1 ton = 1000KG.

10X+400=5000

The solution is X=460.

25×5000- 1000=Y

Y= 124000。